is there a bigger piston available?

I use to have a cylinder boring business, and have helped many hundreds of people rebuild their two stroke top ends .... including dozens of DT360 cylinders.

Personally, I've never seen or heard of a problem boring these up to 82mm

I've only recently heard (on another site) one guy claiming anything larger then 80.75mm could be too much.

I can not guarantee someone else's work, but if the piston to cylinder clearance is finished to .0016 of a inch, I would not be worried.